This invention relates to cutting or abrasive working operations, particularly to metal, cermet, or composite cutting or abrasive working operations, and more particularly it relates to working fluids comprising one or more hydrofluorocarbon(s) and one or more specific lubricious additive(s) used in conjunction with these operations.
Drilling and machining fluids long have been used in the cutting and abrasive working of metals, cermets, and composites. In these operations, including cutting, milling, drilling, and grinding, the purpose of the working fluid is to lubricate, to cool, and to remove fines, chips and other particulate waste from the working environment. In addition to lubricating and cooling, these working fluids also can prevent welding between a workpiece and tool and can prevent excessively rapid tool wear. See, for example, Jean C. Childers, The Chemistry of Metalworking Fluids, in METAL-WORKING LUBRICANTS (Jerry P. Byers ed., 1994).
A working fluid ideally suited as a coolant and/or lubricant for cutting and abrasive working of metal, cermet, and composite materials preferably imparts a high degree of lubricity for the duration of the cutting and abrasive working operation. But the working fluid should also preferably possess the added advantage of being an efficient cooling medium that is non-persistent in the environment, is non-corrosive (i.e., is chemically inert), and does not leave a substantial residue on either the workpiece or the tool upon which it is used.
Today""s state-of-the-art working fluids generally comprise two categories of materials: (a) oils and other organic chemicals that are derived principally from petroleum, animal, or plant substances; and (b) fluorinated hydrocarbons. The first category, i.e., the oils or other organic chemicals, commonly are used either neat (i.e., without dilution with water or solvent or are compounded with various polar or chemically active additives (e.g., sulfurized, chlorinated, or phosphated additives). These neat or compounded materials are also commonly emulsified to form oil-in-water emulsions. Widely used oils and oil-based substances include the following general classes of compounds: saturated and unsaturated aliphatic hydrocarbons such as mineral oil, turpentine oil, and pine oil; naphthalenic hydrocarbons; and aromatic hydrocarbons. While these oils (and oil derivatives) are widely available and are relatively inexpensive, their utility is significantly limited, as the oils preferably are non-flammable and consequently exhibit low volatility during drilling or machining operations. These low volatility oils tend to leave residues on tools and workpieces, thus requiring additional processing at significant cost to remove the residues. Emulsified materials also leave residues of surfactants and emulsifiers in addition to oily residues on tools and workpieces.
Fluorinated hydrocarbons, the second category of materials for the cutting and abrasive working of metals, cermets, or composites, has generally included the groups of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and perfluorocarbons (PFCs). Of these three groups of fluorinated hydrocarbons, CFCs historically are the most useful and the most widely employed. See, e.g., U.S. Pat. No. 3,129,182 (McLean). Then HCFCs were used as lower ozone-depleting potential replacements for CFCs following the Montreal Protocol of 1987. CFCs and HCFCs typically used included trichloromonofluoromethane, 1,1,2-trichloro-1,2,2-trifluoroethane, 1,1,2,2-tetrachlorodifluoroethane, tetrachloromonofluoroethane, and trichlorodifluoroethane. The CFCs and HCFCs generally accepted as most useful from this second category of materials possess many of the characteristics sought in a working fluid. While they were initially believed to be environmentally benign, CFCs and HCFCs are now both known to deplete the ozone layer of the atmosphere (See, e.g., P.S. Zurer, Looming Ban on Production of CFCs, Halons Spurs Switch to Substitutes, CHEM. and ENG. NEWS, Nov. 15, 1993, at 12). While PFCs have no ozone depleting potential, they tend to persist in the environment (i.e., they are not chemically altered or degraded under ambient environmental conditions). Also, when used alone, these fluorinated hydrocarbons often do not impart as high a degree of lubricity to cutting or abrasive working operations as do the oils and oil derivatives described in the first category of materials.
Thus, there continues to be a need for a volatile working fluid for use in cutting and abrasive working operations that provides the necessary lubricity for the duration of the operation, but that does not leave a residue on the workpiece. Additionally, this working fluid preferably exhibits low flammability and good environmental properties (i.e., no ozone depleting potential and low global warming potential).
Briefly, in one aspect, this invention provides a working fluid useful for the cutting and abrasive treating of metal, cermet, and composite materials, wherein the working fluid comprises one or more hydrofluorocarbons (hereinafter referred to as HFCs) and one or more lubricious additives, each additive having a boiling point from about 200xc2x0 C. to about 350xc2x0 C. In another aspect, the present invention provides a method of cutting and abrasively treating metal, cermet, and composite materials, comprising applying to the metal, cermet, or composite workpiece and tool a working fluid comprising one or more HFCs and one or more lubricious additives, each additive having a boiling point ranging from about 200xc2x0 C. to about 350xc2x0 C.
The working fluids used in the cutting and abrasive treatment of metals, cermets, and composites in accordance with this invention advantageously provide efficient lubricating and cooling media that fit many of the ideal characteristics sought in a working fluid: efficient lubrication, heat transfer properties, and volatility during the duration of the treating operation, non-persistency in the environment, and non-corrosivity. The working fluids also do not leave a substantial residue (preferably no residue) on either the workpiece or the tool upon which they are used, thereby eliminating otherwise necessary processing to clean the tool and/or workpiece for a substantial cost savings. Because these working fluids reduce tool temperature during operation, their use often also enhances tool life. The addition of lubricious additive increases tool/workpiece lubrication, which minimizes the production of heat from friction, further extending tool life and producing better surface finishes on the workpiece.